Oil Pressure Problem

djester · Post by **djester** » Sat Mar 27, 2010 2:22 pm

My truck had good oil pressure --30-40psi -- warm. Started one day and the oil pressure went to zero. Disconnected line to gauge and very little oil flow, if any, with engine running. Disconnected line at block and blew out and was clear. Reconnected line to gauge, oil pressure came up to about 40, then went to zero.

OK, figured I had an oil pump failure and replaced it. Same problem. Doesn't seem to have any pressure at the gauge line at the block. So I pulled the pan and the bottom of the engine looks brand new. No apparent blockage at the pickup screen.

Ran out of time, so I haven't pulled the pickup and lines to see if there is an obstruction, but I'm running out of ideas.

Any thoughts from you experts? BTW, new gauge, but was working fine when first put in and, in any event, there is no pressure in the line.

Dave

M-Thrax · Post by **M-Thrax** » Sat Mar 27, 2010 2:48 pm

Blank

MSeriesRebuild · Post by **MSeriesRebuild** » Sat Mar 27, 2010 6:26 pm

If a check of the relief valve assy reveals nothing, the usual way of this situation is this. Oil pressure will be lost more so at the cam bearings than anywhere else is the typical find. Usual thing, there will be erratic engine operation / performance, especially at higher RPM's due to the camshaft not running true in the bore. Hopefully the relief valve inspection will source a problem that will be an easy fix for you. The fact that it happened all of a sudden may actually be a good sign.

If it doesn't my next step would be to perform a compression test, while this will check absolutely nothing concerning oil pressure, it will offer a very accurate analysis of the over all engine condition. If the readings are on the low end of the spectrum, that is a good indication that it is time to think about a complete overhaul instead of trying to source only the low oil pressure issue, as that would be addressed when rebuilding anyway. Low compression readings along with low oil pressure generally go hand in hand in a well worn engine. Good luck.

djester · Post by **djester** » Sat Mar 27, 2010 7:00 pm

Thank you gentlemen. At least I now have another possibility to check out.

I am no mechanic, but I had a very experience guy working with me, and we both agreed that it looked like the engine was being well oiled. I don't know if that means anything, but certainly didn't look like any of the surfaces were lacking in oil, every surface was drenched.

Appreciate the help. BTW, are the oil pressure relief valves readily available?

Dave

cuz · Post by **cuz** » Sat Mar 27, 2010 10:15 pm

Over the years I have on several occasions ran that problem down to blockage in the oil gallery that feeds the gauge line. Disconnect the block fitting, blow the gallery out and connect a direct reading gage directly to the block and fire her up.

Glenn · Post by **Glenn** » Sun Mar 28, 2010 4:07 am

I'd bet on the relief valve being stuck in this case. More than likely just gummed up.

djester · Post by **djester** » Sun Mar 28, 2010 6:40 am

Well, tomorrow we'll tear it all apart and see what we find. Sure hope it is the relief valve.

Bought this truck a couple of years ago for $600, after it had been sitting in a barn yard for a number of years, rusting away, but in reasonably good shape. First thing we did, of course, was to see if the engine would run. After new plugs, wires, ignition, gas, and fluids, it fired right up, with good compression.

Since then it has only run a few times to move it around during restoration, or just to exercise the engine. Always starts and runs without a problem. Now just about ready to finish up, after blasting, painting, new gas tank, brake and fuel lines, and wiring harness. Just as I was ready to take it out for a few miles run, this problem happened. What a bummer!

Oh, well, keeps me out of bars . . .

Dave

RobertTX · Post by **RobertTX** » Tue Mar 30, 2010 4:07 am

A friend almost lunched a fresh engine due to a cracked pickup tube. The crack was not easy to see, but let the pump suck air when the engine was running.

powerwagontim · Post by **powerwagontim** » Tue Mar 30, 2010 7:52 am

Hi Dave,
Lots of times an engine that hasnt been run for many years will start up and run, but then all of the years of crud start screwing things up and she goes down hill fast.
Tim

djester · Post by **djester** » Tue Mar 30, 2010 2:23 pm

I understand your comment Powerwagon Tim. However, after opening up the bottom end of this engine, it looks new. Not a speck of sludge or rust, and the cam doesn't show any wear.

The end result of this adventure, after tearing the oil system down as much as possible, replacing lines, cleaning and blowing everything out, we couldn't find any thing wrong. Imposed upon Charles Talbert and AB Linn to get their expertise far too much, but we couldn't come up with a cause.

So we put it all back together and now I have fantastic oil pressure! Can't really say what we did to fix it. Almost too much pressure, if that is possible: cold about 55psi and warm about 35-40. Not sure what to think about that . . .

Appreciate all the help, learned a lot about this old truck in the process. Much more comfortable with it now. Heck, if I had the time, I think I'd drive it to California. Nah!

Dave

MSeriesRebuild · Post by **MSeriesRebuild** » Tue Mar 30, 2010 2:33 pm

djester wrote:I understand your comment Powerwagon Tim. However, after opening up the bottom end of this engine, it looks new. Not a speck of sludge or rust, and the cam doesn't show any wear.

The end result of this adventure, after tearing the oil system down as much as possible, replacing lines, cleaning and blowing everything out, we couldn't find any thing wrong. Imposed upon Charles Talbert and AB Linn to get their expertise far too much, but we couldn't come up with a cause.

So we put it all back together and now I have fantastic oil pressure! Can't really say what we did to fix it. Almost too much pressure, if that is possible: cold about 55psi and warm about 35-40. Not sure what to think about that . . .

Appreciate all the help, learned a lot about this old truck in the process. Much more comfortable with it now. Heck, if I had the time, I think I'd drive it to California. Nah!

Dave

You don't have too much pressure, the range you spoke of is right where it needs to be both cold and warm. Glad you got it going.

djester · Post by **djester** » Tue Mar 30, 2010 2:46 pm

Charles, I'm sure this stuff is old hat to you, but I doubt you know how many questions you answered for us in this quest. Your patience and understanding is remarkable. I owe you big time, thanks!

Dave

MSeriesRebuild · Post by **MSeriesRebuild** » Wed Mar 31, 2010 8:39 am

djester wrote:Charles, I'm sure this stuff is old hat to you, but I doubt you know how many questions you answered for us in this quest. Your patience and understanding is remarkable. I owe you big time, thanks!

Dave

Well I'm glad I could be of help, anytime.

Rich · Post by **Rich** » Fri Apr 02, 2010 6:18 pm

Djester,
I had a similar problem with my oil pressure, in a parked position on level ground I had 35 psi on the guage, When I pressed on the clutch put it in 1st gear and let out the clutch it would go to zero when the truck moved. I removed the sending unit and put a mechanical guage on the engine and it had 35 psi. I cleaned the electrical sending unit inside the tube with the breakkleen and blew it out. I also made sure it was cleaned on the outside so it had a good ground. When I reinstalled the sender it worked, not just in a parked position ,but when driving.
Rich

djester · Post by **djester** » Fri Apr 02, 2010 7:31 pm

Rich, as I said, I'm not sure what we did to fix the problem. My M37 has a mechanical gauge and with the engine running a very little oil would run out of the line at the gauge. We cleaned and blew out the line, but had the same result, including coming out of the block where the tube attaches. Obviously, there wasn't any pressure.

Charles suggested that the rotor at the top of the pump might be the problem, but since I already had a new pump, we put it on. I suspect he might have hit on the problem, but haven't torn it down to see its condition.

Of course, as previously said, we cleaned and blew out all the lines, checked the relief valve, and replaced the gauge, so it is hard to know exactly what it was. I suspect it was the pump, however, even though looking at it it seemed to work and had no apparent wear on the gear.

Dave